See my post above - Spark Cash goes to Venture X directly - but only to your own

If you have a cash back card you can send to others cash back card only - So Spark to Spark is OK
Then you can move all to your venture X

What you cannot do is more Your wife's / friends Spark Cash direct to your Venture X
So I now keep a no fee Spark Cash back business card along with a Venture X in the account of the person who transfers to airline miles

So - Spark --> gift / transfer to anothers Spark -> same user Venture X > same user Airmiles is OK
or Cash PLUS gift / transfer to Spark - > same user VentureX -> same user air miles is OK
or or Cash PLUS gift / transfer to Spark Miles -> same user VentureX -> same user air miles is OK

AFAIK You need to keep a cash card and a miles card in the same primary users capital one account for maximum flexibility
e.g., 300k Cash Plus offer for 50k spend = 100k more = 400k in cash Plus - can not be sent to Another persons Venture X directly (although I had success once as a manager - but that might be an exception)
It can be sent to another's Spark Business then to same person's -> Venture X or Spark Miles or I suspect Elite PLUS in future

Combining points - unlimited amounts seem to be OK so far and can be sent to anyone - but needs their card number ! - so be careful who you give card number to !
I did manage to send to an AU card by calling Cap 1 and it went to the primary users account
Cash can be sent to another's cash back card by calling Cap 1
Miles can be sent to another's miles card by calling Cap 1

Inside your own account
Cash to Miles is one way; but you can get a statement credit if you like for your miles card account - at 1c
Miles can not be sent to a cash back card account directly and / or sent to another's cash back card
Miles can only be sent to Primary cardmembers airmiles account (unlike Amex which can send to an AU account after 90 days)

Managers and Users
Cap 1 does not allow online access for AU unless it is a manager - only 1 manager per account
Manager can see details of all charges and rewards in the account and can see the points but can't transfer them to airmiles
e.g.,
I was manager on a Venture X account - I could not transfer the points to my own airmiles account - Venture X account the PU had to call to send to my Venture X card profile
I was manager on a Cash PLUS account - I could not transfer the points to my own Spark cash account the PU had to call
In both cases, I had to make the PU call and then once the points were in my cash account I could combine with my Venture X and then to airmiles

Problems with Capital One miles ease of use by partners
- Singapore Airlines allows only 5 users for whom one can book - I used up 5 users for my brothers family from LHR to SYD on J and F
- Now I can't book for SQ for my own family for 6 months - and I have to pay for each user to be changed
- so now I need a Venture X for my spouse - to transfer to SQ to use for our own family

Aeroplan, Emirates Turkish and SQ have been quick
My first transfer of 500k to Emirates was held up as fraud - came back to me but I had changed my mind by then - I called to reverse it and was refused!
The miles came back as fraud alert - since then transfers of 100-200k go through with no problems
SQ 500k after several smaller transfers went off fine

For almost all airline partners that other banks have Cap 1 allows ease of transfer at a much lower cost due to 2x earn - lost cash back cost of max 1.3c (2.62cash back vs 2 points per $ spent)

Allows Combining cash or points with anyone else for free with no obvious issues or shutdowns so far that I know of and I have done several large ones in 6-7 figures
- Main issue - the primary user has to call - and need to know recipients numbers
- better than Citi - expiry of transfer points at 60-90 days - but you only need TY points number not CC number
- better than Chase - restricted to family mainly for personal cards or partners / owners for business cards
- better than Amex - no transfer or MR points (but transfers to airlines ok for AU)
- Obvious Exceptions
AS - BofA cards
AA - Citi / Barclays cards
DL - Amex DL and MR cards
UA - Chase UA and UR cards
WN - Chase WN and UR cards
KE -US Bank only
LH - Barclays only

EDITED NOV 2022