@kenneth80336 could be a dirty speaker mesh or a bad speaker. Clean the opening for the speaker with a stiff nylon brush (something like a new toothbrush) and see if that works. If not, then it is most likely time to replace the speaker. Since iFixit does not yet have a guide for this, use something like the one [https://www.nadiemellamagallina.com/en/manuales/smartphones-1/xiaomi-191/xiaomi-redmi-9-1289/altavoz-11489|from here] It works for your phone as well. It was written in Spanish so use a browser that does the translation for you. Replacement speakers are readily available at many online stores.