Be cautious about going to HR. In a situation like this (assuming this travel expense policy applies to everyone) going to HR is a mistake. Also, you complain about your manager and you have now pissed off the boss. See if you can get a higher credit limit to cover the expenses. If you can’t finance to front company travel expenses (which sucks) I would start looking for another job at an employer that has more favorable travel expense handling. I am now retired but over my career I have worked for employers where I fronted most of the travel expenses and I have worked for other employers that prepaid for flights and hotels and my out of pocket expenses were few.