Within my social circle it differs between groups, so some work with the 'if we invite then we're paying' mindset, whereas another group have always been let's go out for a meal and every pays their own bill.
I'm happy with either, although if your guests would expect you to pay at their celebration then they should expect to pay at yours.
Consequently, those that have paid for you before could possibly be a bit miffed at expecting to pay for themselves.
IMHO, it's very individual, even within families, etc, so the only way to avoid embarrassment is to be very clear upfront.
I would rather know/tell people beforehand, as it may be that people can't really afford it but think you're paying so will have a shock when the bill comes and wouldn't have said yes to coming if they'd known.
Personally, if I now invited people for a meal to surprise DH for his birthday, I'd expect to pay for everyone, especially if it was family.
OTOH, we have had years previously where we've wanted to celebrate, but wouldn't have been able to pay for everyone, but we've then said on the invite, something along the lines of we're eating at X to celebrate Y's birthday, if you want you're welcome to join us but will have to cover your share of the bill.
Hope you get it sorted.