Below are the formal and polite equivalents (synonyms) of 'happen' which you can use in your business or professional pieces of writing.
The below synonyms can be used when you want to explain to somebody what, why, when and where something 'happened' or 'will happen'.
This is normally only used for explaining when, where and why negative things (e.g. problems, accidents etc...) or changes 'happen'.
'A problem occurred in one of the machines in the factory.'
This can be used in all the same ways as 'happen'. It sounds a little more formal.
'The presentation will take place in the civic centre on Tuesday the 1st of March.'