Welcome to the community @Richard-Dodo 

As you say, a profile will only enter a list-triggered flow once when they become members of that list (same for segment-triggered flows). 

So there are two approaches to your use case:

1. Seperate list. Create a seperate list for Lead Magnet B that triggers that flow and your LMB form pushes to that list. Contacts submitting LMA will enter the LMA flow and if they also submit LMB, they will enter the LMB list/flow .
2. Custom property + segments. On your forms you have a custom property called ‘lead_magnet’ with a ‘list type’. For example, on the Lead Magnet A form you push the value LMA to this custom property and push LMB on the Lead Magnet B form. You then create segments for LMA and LMB and trigger your two flows from those segments.

My preferred approach is 2 as it will maintain a single list and the custom property, because it’s a list type, will capture the all the values - LMA and LMB - on profiles who’ve submitted that you can easily use for future segmentation. Also better if you are to add LMC, LMD etc at some point.

One consideration regarding timing is segments don’t update immediately, as “close to real-time as possible” according to Klaviyo, whereas list updates do. I’ve never run into any segment delay issues though.

Hope that helps

Andy

Just to add to the thread here, if you have two separate Klaviyo Signup Forms, one for Lead Magnet A, and another for Lead Magnet B, then there is a new Klaviyo API metric called “Form completed by profile” that you can also use for a metric triggered Flow.  I see this in most of my accounts, but verify if you have that metric by going to Analytics → Metrics → Search “Form” and you should see this:

Then, you can create a Metric Triggered Flow based on that metric “Form completed by profile” to look something like this:

Just note, you want to add the Trigger Filter for the specific form_id for the respective Signup Form for your Lead Magnet A, then duplicate this Flow for Lead Magnet B and changing the form_id.  That way, depending on which form they completed, they will go to the respective Flow (one for Lead Magnet A, one for Lead Magnet .

Since this is a Flow triggered by a metric (and not a List or Segment), users can enter either one (or both) as many times as they complete Signup Forms - and each time they do so, they will go through the Flow to receive the messages in the Flow (e.g. Sending Lead Magnet A).

I use to do it the way @bluesnapper suggested, but if you have this metrics, this is great for certain circumstances where you may want someone to be able to go through multiple signup forms (or multiple of times).  

Hope this helps!

Joe