Every WhatsApp business number has a quality rating (high, medium or low) based on how customers react to your messages: blocks, reports and the reasons they give. A high or medium rating plus steady sending moves you up the tiers. A low rating can stop upgrades, and if it stays low Meta may lower your limit or restrict template sending.
The ways to keep quality high are simple: message people who asked to hear from you, keep messages relevant and not too frequent, personalise them, and always give an easy way to opt out.