Ex wants to stop paying for DC whilst so he can get a mortgage

I think everyone else has covered the main points with this one but as an aside, how the hell has he got himself a Mercedes for only £150pcm?
I presume it’s not new? 2nd hand with some sort of loan?

Tell him the payments have to be by bank transfer - it needs to show up on his statements, so potential mortgage lenders will see what his true outgoings are. If that doesn't happen, you'll be going the CMS route. Honestly - he's begging milk and bread from you, and he thinks he can get a mortgage? Never give him so much as a tin of beans again - any spare penny you have, use it for the benefit of your kids, not him. Do whatever you can to support them, because he's never going to.

Another point to consider - how do you know he's being honest about who much he gets paid?! He could well have lied and be paid more. Which would be another reason he'd want to avoid CMS!
Agree with @PinkLegoBalloon this is a person who will tell you whatever he thinks you'll swallow, but when you stand back & look at his behaviour it's not hard to read him.
His main talent is persuading you to feel sorry for him OP!

OP just decline the request to pay you cash. State you need it paid directly into your bank for you bills.

Funny how he has now paid you after you showed him you'd been on the CMS calculator! My bet is he will strongly want to avoid that, as any efforts to use the maintenance as a form of control will be MUCH harder to do with CMS involved.

Another point to consider - how do you know he's being honest about who much he gets paid?! He could well have lied and be paid more. Which would be another reason he'd want to avoid CMS!

No more meals cooked, no more grocery hand outs, etc.

I have leant the hard way that being nice gets me nowhere with this man, if anything it makes him worse
@fedupofex
He experiences kindness as weakness and his urge to exploit you is strongly triggered. This man will do whatever he feels he can get away with, I hope you can carry on with the refusing him and shutting him down.

Tell him a proper man would support his children with living expenses, engagement and actual parenting.

Tell him a proper man would be a responsible adult by 43 and be able to prioritise his responsibilities over status cars and that his kids don't need an inheritance of a house from him, but their needs met in the here and now.

Tell him if he's worried about not having property and economic success by his age then he needs to grow up, stop feeling entitled to demand handouts from family, develop some financial nous, get rid of his expensive hp car, hold down a job and get a mortgage realistically without committing fraud.

So glad he's your ex

He can’t afford a mortgage.

He needs to pay for his children.

its not your problem. Say no.

Say no, I need the money to go into my account as my bills are not paid in cash.

Nope

All through the bank please buddy so it's transparent.

Sod him. Sounds like a total arse.
Or.... Just let him commit fraud, and then tip someone the wink.

Misclicked meant to say NU. Anyone who gets a new Mercedes can pay your child support still.

Unfortunately Courts don't deal with CMS. They also can't make a parent parent if you want him to see them more. They only deal with Child Arrangement Orders, however, if you have a CAO in place for when he sees the children, you could ask the Court if you can share that with CMS to calculate the payments.

Even if it’s £15 less, if you go through CMS he will pay it every month so you won’t have to worry about not receiving anything or having to ask him repeatedly.

Ask yourself, do you honestly think he would give you extra food if you were struggling? If not, why did you give him anything? You are giving away your children’s food to a manipulative bastard who has treated you very badly. Stop thinking of him as being your responsibility in any way.

How is he going to cope with subsequent mortgage renewals every few years.
What he’s proposing is fraud.

No it doesn't work like that.

His kids come before a new car so why wasn't he equally worried that the car HP would affect his mortgage application?

What a cheeky so and so.

Don’t weaponise your kids, they should continue to see him if they enjoy it.

but wow, what an utter loser.

Tell him that a proper man would prioritise supporting his children, and would not need to be chased or chivvied about doing so.

I assume the (new to me) phrase "children aren't pay per view" - quoted several times on this thread - was originally coined by some utter twat of a bloke who wasn't paying maintenance for his children.

Go through CMS. The less you have to deal with this nasty person the better.

"Visiting" his children - nope, he should be parenting them. Actually having them for a period of time including overnights, ferrying to and from activities and later on, school with cooking and washing for them and spending quality time with them. Trouble is, he doesn't want to do any of that and does literally visit them for a few hours and OP can't do anything useful for herself in that time as he is in her home so still doesn't get any time off from parenting. He's a waste of space and dishonest as well. Least of all he could do is pay for them but no, he'd rather pay for a car...

He needs to pay the maintenance. End of.

He needs to be able to afford the mortgage and his CM payments so this is clearly a bad idea. Why would you help him over commit himself six that he can’t afford to support his children?

100% this. What a dumbarse. Good news that he is your ex OP 👏

How’s he intending to not show the cars HP payments on his bank statements.

He sounds like an entitled child.

If he wants a house like you then go out and rent one