sticking point

US /ˈstɪk.ɪŋ ˌpɔɪnt/
UK /ˈstɪk.ɪŋ ˌpɔɪnt/
"sticking point" picture
1.

a point in a discussion or negotiation at which no further progress can be made because of a fundamental disagreement

:
The main sticking point in the negotiations was the budget.
We reached a sticking point on the terms of the contract.