IBKR registers bonds in "street name" which means that interest payments are made from the issuer to IBKR who, in turn, deposits the payment directly into the client's brokerage account. This is generally processed on the coupon payment date, but can be delayed slightly when occurring on a non-business day or if the funds have not yet been received from the issuer or depository/agent.
To see the coupon payment details, log in to Client Portal to launch an Activity Statement and refer to the ‘Interest’ section. Note that the payment will be reflected on the statement for whichever day the coupon was actually received and posted to the account.