Popup integration

Sub2 offers easy checkout integration with a popup window. It works by opening a URL starting with www.sub2protocol.com/popup followed by URL arguments. This makes it possible to create a custom button or other HTML elements on your website while still preserving all functionality in a separate window. The list of arguments can be seen here:

Parameter	Details
recipient	Address of the recipient of the subscription payments.
cooldown	Number of seconds between payments. For example, 30 days is cooldown=2592000.
token	Address of ERC-20 token that is paid with.
amount	Amount of tokens paid each time. This is the actual decimal number e.g. amount=10.5 and not the EVM integer version.
processing_fee_token	Address of the ERC-20 token used for processing fee.
max_processing_fee	Amount of maximum processing fee. This is the actual decimal number e.g. max_processing_fee=0.02 and not the EVM integer version.
auction_duration	Duration of the auction period in seconds. This has to be less than or equal to cooldown.
initial_delay	Delay in seconds before the first payment is due.
initial_payments	Number of initial payments with the creation of the subscription. If initial_delay > 0 then no initial payments are made.
sponsor	Address of sponsor of the subscription.
sponsor_signature	EIP-712 signature of sponsor permit. The permit has to contain the same parameters as given in the URL.
permit_nonce	Nonce of the sponsor permit used for the signature.
permit_deadline	UNIX time in seconds for when the provided sponsor signature will expire.

The parameters sponsor, sponsor_signature, permit_nonce and permit_deadline should only be provided if there is an intention to sponsor the processing fee of the subscription. However, if there is an intention of making a sponsorship, all of these parameters should be provided.

Note that there is no field for sender/subscriber. This is because the user should be able to chose which account they want to pay the subscription with.