This is the 17806th most frequent Russian word.
уплачиваемого
"Payable" or "being paid."
In this sentence, "уплачиваемого" is a form of the verb "уплачивать" (to pay), converted into a passive participle to describe the tax that is being paid.
Размер уплачиваемого налога зависит от дохода.
The amount of the payable tax depends on the income.
Here, "уплачиваемого" refers to a contribution, describing it as something subject to payment, using a passive participle.
В документе указывается порядок расчёта уплачиваемого взноса.
The document specifies the procedure for calculating the payable contribution.
In this example, "уплачиваемого" modifies "штрафа" (fine), indicating that it is a fine to be paid.