You’ve presumably had legal advice because you know that an N244 is required to try and suspend the Order to one on payment terms, but Shelter has some further info if not.
https://england.shelter.org.uk/professionalresources/legal/possessionandeviction/evictionoftenantsofmortgageborrowers
I dont have time to advise in detail, but you will need to provide the following with the N244 (and take it to your court hearing) as an absolute minimum:
-Reliable, detailed proof of the sale. Take the property listing advert, and any correspondence which confirms the agreed sale price and stage you’re at with the sale.
-A comprehensive income and expenditure form (check the CAB or a debt website for a good pro forma) showing that it is affordable for you to continue paying the mortgage in full for the time being. Take very recent evidence of your income to support this for at least a three month period - payslips, bank statements etc.
-In an ideal world, you’d also be paying an amount towards the arrears. The minimum generally considered acceptable is the ‘Norgan rate’, which is the total arrears divided by the mortgage term remaining. So, for example, if your arrears were £2000 and you had a 24 month term remaining, the minimum acceptable arrears repayment would be £83.33pcm.
-If you cannot afford to pay the mortgage in full at the very least while the sale proceeds, it’s going to be much harder for you to get a stay of execution, even if you do have considerable capital in the property. Clearly, this is because the sale isn’t guaranteed at this stage. I think your best bet at that point would be to clearly evidence what you can pay for the time being, and to make the obvious arguments about how you’re likely to cheat the debt quicker/ get a better price for the property etc if you, rather than the bank, can take charge if the sale.
Make sure you speak to the duty solicitor prior to your hearing, get there well in advance so they have time to assist you.
Good luck