Is it permissible to file a lawsuit in legal – non-Sharia – courts to reclaim rights from a procrastinator and swindler, or is that a violation of Islamic law?

The default rule is that it is impermissible to resort to man-made laws for judgment, as they contradict the rulings of Allah. However, it is permissible to resort to them when there is no other way to obtain one's right, provided that one does not claim more than the legitimate right. Based on this, there is no objection to claiming compensation for damages resulting from the delay in completing the agreed-upon work, if the specified period was conventionally sufficient, and if reconciliation is not possible, it is permissible to resort to secular courts. The penalty clause is valid, and it is permissible to claim it, but one may only take from it an amount equivalent to the actual damage incurred. If no damage occurred, then one is not entitled to take anything. However, if the stipulated period was insufficient, the condition is void due to gharar (excessive uncertainty).