I’ve never seen this in my life and looks extremely suspicious to say the least and If I were your lawyer would advise completey against paying upfront all IVA/VAT, it’s ludicrous.
In a deposit you always pay an amount of money and the proportionate 7% VAT for a new build/off-plan. But you never ever pay all the VAT upfront. No developer would or could ask for that. That’s the EA meddling.
It’s not illegal providing you agree to it but it’s certainly not advisable. The only reason I see to doing this is that the EA is needing cash badly and has “forced” you to do this.
Did your lawyer advise or let you do this ??¡¡¡!!!