It is not Adharma to charge or pay interest.
Manusmriti 8.140 to 8.142 says the following
The money-lender shall stipulate an interest sanctioned by Vasiṣṭha, for increasing the capital. He shall take monthly the eightieth part of a hundred.—(140)
Or, remembering the duty of the righteous, he may take two in the hundred; by taking ...