It is a mandatory statement regardless of the type of craft invoice.
Good that the OP only has a partial payment and not a partial invoice at first. And with partial payments, usually only a percentage value is indicated. Public clients also usually do not like it that way because, according to VOB, the verification is made more difficult. But it is quite common.
And whoever agreed a lump sum price with the OP will be able to have the final invoice look like this according to VOB:
"Based on the contract dated __________ for the provided
service __________, the agreed lump sum price is
charged."
The client has no legal claim to a detailed invoice here.
The question is whether the OP wants to put up with the hassle with the electrician.