Not drinking from the bottle

I’ve gone back to work this week and my partner is now the full time parent. My bub is 7 months old and EBF. We’ve given bottle of expressed milk in the past when I’ve been out for a few hours and he has taken the bottles absolutely fine. We even tired formula the weekend before I went back just to see if he would take before I head back. He drank 6/7 ozs fine. But since Monday he just isn’t taking the bottle for his dad. Today he drank barely 5 ozs from my last feed at 5am until when I got home at 5:30pm. My partner said it was a real struggle all day and he would just play with the bottle, get frustrated and then refuse. He breastfed as soon as I got home for 10 mins and then did a very long feed before sleep. He’s on solids too and puts away quite a lot for breakfast but obviously we know the milk is most important at this stage. What should we do when he’s just refusing the bottle all day???