The way I remember business package rates are as follows:

Part of the room rate is taxed with 7%, another part is taxed with 19%. That other part contains things like breakfast, internet, use of business center and similar (basically things that try to hide the breakfast charge).

If that other part is 28€, I see no problem if the OP charges 100€ to his employer and pays 13€ by himself. It's tax-neutral and can be backed by a screenshot from the online reservation (100€ + 13€ additional for breakfast). The 100€ are certainly a justified business expense as it would have been incurred whether or not OP had chosen to pay for breakfast or not.

HTB.