yes, only interest can be recovered by the department under section 73 of the CGST Act,2017, becaus of, if differential amount of GST paid after due date as per, tax amount paid along with @18% of short amount as interest u/s 50 of CGST Act.
As per Sec.73(1) reade along with rule 142 of CGST Act ,Where it appears to the proper officer that any tax has not been paid or short paid or erroneously refunded, or where input tax credit has been wrongly availed or utilised for any reason, other than the reason of fraud or any wilful-misstatement or suppression of facts to evade tax, he shall serve notice on the person chargeable with tax which has not been so paid or which has been so short paid or to whom the refund has erroneously been made, or who has wrongly availed or utilised input tax credit, requiring him to show cause as to why he should not pay the amount specified in the notice along with interest payable thereon under section 50 and a penalty leviable under the provisions of this Act or the rules made thereunder.