Pay for geothermal deep drilling immediately or after acceptance by the heating technician?

Normally, the deep drilling should have already been tested by the manufacturer as part of the service - pressure testing using the contraction method, with a protocol. Possibly, this test and protocol are also part of the requirements from the authorities for the drilling permit. The test can also be carried out "on the greenfield", even without the shell construction.

If this test has been carried out, then your drilling is all right, you can safely pay.