WhatsApp's own limits: the daily limit and the quality rating
Meta sets how many new people your number can message a day, and rates its quality.
Updated
Two things about your number are set by Meta, not by Syniria. Both show on the Campaigns page under WhatsApp daily limit.
The daily limit is how many new people your number may message in any 24 hours. New numbers start at 250, and Meta raises it in steps as you send to more people and keep a good rating. A campaign larger than the limit goes out over several days, showing Waiting for daily limit in between; you don't need to do anything.
The quality rating is High, Medium or Low, and reflects how people react to your messages: blocks and reports lower it. When it's Low, the review step warns you, and a campaign going out pauses if the rating turns red.
To keep both healthy, send only to people who agreed, write messages they expect, and don't send too often.