Contact their customer service and they will tell you where the issue is - this happened to me the first time I used Cashapp and they cited the same reason for cancellation - that it was for my protection. It transpires the issue was with the guy’s account, not mine. (In the end, that particular guy just paid by bank transfer).
Since then, I have used Cashapp successfully for many payments, and have never had to have anyone transfer £1 ahead of the full amount.
MissStar - no, £180 isn’t too much to transfer all in one go, I’ve successfully received payments of 1K with no problems!