Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Get emergency help if you cannot pass urine at all and have significant lower abdominal pain.
Seek urgent medical advice if you can pass only a few drops despite a strong need to urinate, particularly if your lower abdomen is becoming painful or swollen.
Fever, chills, vomiting, confusion, or feeling very unwell alongside difficulty urinating also requires urgent assessment because infection and blockage can occur together.
Seek prompt help if a catheter stops draining, falls out, or is associated with worsening pain, fever, heavy bleeding, or large blood clots.
Arrange a routine appointment if you develop a persistently weak or spraying stream, need to strain, take much longer to urinate, or repeatedly feel that your bladder has not emptied.
Recurrent urinary infections, blood in the urine, or steadily worsening symptoms also need assessment.
The article also says
After a procedure, follow the specific contact instructions from your surgical team.
Every sign above is quoted from the sofidex article on Urethral stricture. If you are not sure, err upward — it is always reasonable to be checked.