The essential guide for players and clubs at every level (Provincial, National, Amateur & Pro) on transfers, regulations and fees.
Every year, footballers with an amateur status (including Provincial and National leagues) can resign their membership at their current club in April to become a free agent. This is the only time in the year when you can leave without your club's approval. (Professional players, e.g., in 1A and 1B, follow official FIFA/UEFA transfer windows: summer and winter).
Digital (Recommended): Via the website of Voetbal Vlaanderen or ACFF. You need your eID and card reader or Itsme. This is the fastest way and you immediately receive proof.
Registered Letter: Only necessary if digital does not work. The letter must be sent between April 1 and 30 to both the RBFA and your current club.
After resignation, you are free. You can sign with a new club starting May 15. For field football, this must be done before August 31 to be allowed to play in the first team at the start of the season.
At the amateur level (like Provincial and Regional), no direct transfer fees are paid between clubs for players. There is a system of training compensation regulated through the association ("the pool"), which is based on age and training history. In professional football (and depending on the contract in higher National leagues), transfer fees are negotiated.
Most players in Provincial and lower National leagues. You only receive expense allowances (match bonuses). There are strict maximums (e.g. €4,500/year limit for reduced tax burden).
An employment contract (part-time or full-time). Social security and taxes are paid. Common at professional clubs (1A, 1B) and higher National leagues (like 1st and 2nd National).
Need more details? Consult the official sources.