minute of agreement

voluntary maintance for child included in Minute of Agreement signed/divorced 2 years ago. Daughter was 11 at the time....
at no point during discussions with lawyers did my ex want to discuss access weekly or holiday.....was simply I will pay xxx for maintenance for daughter until she reaches 18 or leaves FTE.....payments were to increase each year.....however I have not bothered with the increases..as voluntary arrangement which is bit more than CSA would have arranged so Im happy with this.....

However ex now wants to reduce pmts
(1) he claims to now not be able to afford...which im finding hard to believe
(2) he wants daughter to live with him 5 nights a week - which will cut the money he pays as well........

How does this work when a voluntary arrangement is built into a minute of agreement -

Does he have to prove he can no longer pay this...would he have to provide evidence...
would it be possiable to monitor things so that if he was once again able to pay what was agreed he would start paying this....

I dont trust ex....he is in very privilaged position where by he can manipulate things to suit him.....

when a agreement like this is in place...
can someone decide of their own back to just reduce or stop paying without evidence to prove their circumstances have changed...if lifestyle changes could be taken which would allow them to continue making pmts could you insist someone do this or at least prove why they cant....
How legally binding is a Minute of agreement....
If payments go down or stop - what action should I take....
Can I do anything myself to keep legal costs to minimum....

Have just read this....

When the Separation Agreement has been in place for a year either party can apply to the CSA if the child qualifies, the CSA notifies the court and the separation agreement ceases to have any effect......

When parties agree to a voluntary maintenance agreement and it is built into the minutes of agreement so the divorce can proceed - whats the point when they only need to keep to the agreement for a year....

Great idea when someone needs divorce in a hurry....make the minutes of agreement look good - fools everyone - then after a year they can say well i dont fancy paying this agreed amount anymore id pay less if i went via CSA so thats what im going to do.....

Starting to wonder why I spend 4k on lawyers to try to get the minute of agreement right

ex married 7 weeks after papers were signed...no wonder it had to look good on paper....