He has bubbles in his eye as well, so it may be a respiratory/sinus disease called mycoplasma (MG.) Have you seen him sneezing or having noisy breathing? Have you added any new birds to the flock in the last couple of weeks? I would buy some Tylosin from a pigeon site online, if you cannot get it from your vet. Dosage is 1 tsp per gallon for 5 days. Here is where you can get it:
https://birdpalproducts.com/products/tylosin-powder-for-birds
Here is some reading about MG:
https://extension.umd.edu/sites/extension.umd.edu/files/2022-04/FS-1008 Recognizing and Preventing Mycoplasma gallisepticum (MG) Infecti....pdf