The field “SE withheld from customer” in the invoice list and in the invoice tab of a project must (at least also) display the proportional SE of the respective invoice so that the sum of the SE is not much too high for cumulative invoices. Alternatively, it should be possible to display two fields (cumulative SE and fractional SE) in the lists and when entering a partial payment amount.

Johannes also urgently needs control over how security withholdings for partial payments on advance invoices are handled.

Security withholding in the construction industry, clearly what Johannes said (in case it helps): https://www.haufe.de/finance/haufe-finance-office-premium/baugewerbe-62-sicherheitseinbehalte_idesk_PI20354_HI1464960.html

Security deposit in case of down payment

Since sales tax is only accrued upon inflow on a down payment, there is no sales tax on the security deposit. The recipient of the down payment only has to exclude the sales tax from the amount that actually accrues to him. The beneficiary — insofar as he is entitled to deduct input tax at all — can only deduct input tax to the extent that he has actually paid the down payment.

Security withholding for performance or partial performance (e.g. security withholding in the final invoice)

Sales tax is incurred by a legally taxed entrepreneur (debit tax) upon expiry of the VAZ in which the service was carried out. As a result, the security withholding must also be taxed. In this respect, the security deposit is only a form of payment agreement. Something else only applies if the security deposit cannot be replaced by a bank guarantee — in this case, the providing entrepreneur should not pre-finance the sales tax for several years.