Does Activemerchant Support Subscription Based Transaction

Recurring payments with ActiveMerchant + Stripe

Stripe implementation at ActiveMerchant doesn't support recurring/subscription payments. In fact, most of the ActiveMerchant gateways integrations are with Shopify in mind. And 99.99% of Shopify transactions are one time transactions.
Take a look at the PayPal recurring solution at ActiveMerchant and you'll realize AM hasn't been focused at all on subscriptions.
Disclaimer: I work at MONEI.

Paypal, Recurring Billing, and ActiveMerchant

Express Checkout is the same as Website Payments Standard. It is the method of redirecting your customers to PayPal to collect their payment info. There's a simple implementation of just creating a form that posts directly to PayPal, and you can optionally use IPN to get info about the transaction. There's also an API for Payments Standard, that lets you set up the transaction with PayPal behind the scenes, then redirect your customer to PayPal, then query PayPal via the API for details on the just-completed transaction. The SaaS Rails Kit (I'm the author of it) uses this API.

Website Payments Pro is PayPal's offering that lets you collect the payment info at your site and pass that info via their API to PayPal. You then get information about the transaction via the API. The customer never leaves your site. PayPal's TOS require you to offer Express Checkout even if you offer Payments Pro. Payments Pro costs $30 / mo. (as I recall) and requires you to fill out an application for a Pro account.

ActiveMerchant/Spree - Is there a per-transaction/per-account commission to the creators?

They don't take a commission.

Active merchant and Paypal API for recurring payment

Usually the "security header is not valid" response comes from using sandbox credentials in the live environment or vice-versa. AM will use the sandbox when your Rails app is in development mode, so be sure you are using the right set of credentials.

When I was integrating PayPal's recurring payment profiles into the SaaS Rails Kit (using ActiveMerchant) I ended up just canceling a user's current profile and creating a new one when they wanted to change their subscription.

How are credit card account cancellations handled by ActiveMerchant recurring payments on Authorize.net?

Looks like the 'right' solution here is to support Authorize.net's 'Silent Post' callback. This will send transaction status on all cleared and failed transactions every night after they're run.

However, the status will only be sent once, so if it's not received for any reason, you'll still need to query subscription status through ARB proactively.

ActiveMerchant's support for determining the account status (verified/unverified) of a PayPal Express Checkout customer/buyer

I used PayPal's paypal-sdk-merchant gem to do the job ActiveMerchant wasn't able to help me with (getting the status of a payer's account: verified/unverified PayPal account. I followed the installation of paypal-sdk-merchant on https://github.com/paypal/merchant-sdk-ruby

gem 'paypal-sdk-merchant'
bundle install
rails generate paypal:sdk:install

Then I set-up their samples https://github.com/paypal/merchant-sdk-ruby#samples. After setting-up the samples, go to /samples of your Rails app and you will find a lot of code generator for what ever function you need from PayPal's API. Don't forget to configure your config/paypal.yml. I configured the username, password and signature (can be obtained from your PayPal sandbox specifically your test seller account) and removed the app_id in my case.

I obtained the following code for getting a PayPal payer's account status (verified/unverified) using PayPal's samples (/samples) and placed it on a class method of a model in my app:

def self.get_paypal_payer_status(transaction_id)
  require 'paypal-sdk-merchant'
  api = PayPal::SDK::Merchant::API.new

  get_transaction_details = api.build_get_transaction_details({
    :Version => "94.0",
    :TransactionID => transaction_id
  })
  get_transaction_details_response = api.get_transaction_details(get_transaction_details)

  get_transaction_details_response.payment_transaction_details.payer_info.payer_status
end

ActiveMerchant recurring payment - cycles parameters has no effects?

I have found it by digging into ActiveMerchant source... The good parameters name is :total_billing_cycles, not :cycles as stated in the documentation that I have...

Work like a charm now :-)