Prayer allowance about to proceed heavenwards (8)
I believe the answer is:
rogation
'prayer' is the definition.
(I know that rogation is a type of invocation)
'allowance about to proceed heavenwards' is the wordplay.
'allowance' becomes 'ration' (I've seen this before).
'about' indicates putting letters inside.
'to proceed heavenwards' becomes 'og' (I am not sure about this - if you are sure you should believe this answer much more).
'ration' enclosing 'og' is 'ROGATION'.
Can you help me to learn more?
(Other definitions for rogation that I've seen before include "Asking" , "Solemn supplication (in Christianity)" , "Solemn petition" , "praying for a good harvest?" .)