To add Stripe as a payment method of your booking form please log in to your back office area and go to Dashboard > Payment methods and click on "New" button in the top toolbox.

Title - type in the name of the payment method as you want it shown to your customers eg. Credit/Debit cards by Stripe, Credit or Debit card etc.
Published: Yes/No - leave to "No" if you are still working on the payment method and set to "Yes" when you are ready to go live. 
Language: All or each installed language for your booking form. If you select a language here the payment method will be available only when this language is selected at the front end booking form by your customers. Useful if you need to show different Title (name and description) for different languages. You will have to create a separate Stripe payment method for each language.
Payment method: a list of all available payment methods - select "Stripe 3DS payment" here ("Stripe payment" is a legacy payment method that is no longer supported by Stripe but still used for some of our older clients, ignore it on new setups). 
Description - type in a description of this payment method that will be shown as a tooltip at the front end if a customer clicks on the payment method name.

Now that you have filled in the basic settings please click on the "Save" button in the top button toolbox. The page will reload and the "Configuration" tab will show some additional fields that are needed for Stripe to operate.
Click on the "Configuration" tab.
Sandbox (test): Yes/No - set to "Yes" if you would like to test Stripe in test mode.
Test Secret Key - get the key from your Stripe's dashboard and paste it in this field.
Test Publishable Key - get the key from your Stripe's dashboard and paste it in this field.
Live Secret Key -  get the key from your Stripe's dashboard and paste it in this field. This set of keys are needed when you move from Test to Live mode by setting "Sandbox (test): No" above.
Live Publishable Key - get the key from your Stripe's dashboard and paste it in this field.
Note: please make sure that your keys don't have leading or trailing white spaces when you copy/paste them as this may invalidate them on the system - simply delete the leading or trailing space and then "Save".
Minimum Amount - set a minimum amount for a Stripe transaction, for example, you may wish not to allow customers to pay with Stripe under $5 so you enter 5 here.
Maximum Amount - set a maximum amount for a Stripe transaction.
Fee per transaction - you may wish to charge a flat fee for each transaction, for example, $1 for each Stripe payment, enter the amount (without) a currency symbol.
TAX in % - here you can add any tax due when using this payment method. Enter the number without the % sign.
VAT in % - here you can add VAT due. Enter the number without the % sign. 
Deposit (%) - you may wish to only charge a portion of the total via this payment method. 100 means 100% (the whole amount), set the percentage accordingly without using the % sign.
Order Status for Pending transactions: Waiting/Accepted/Rejected/Archived - select what will be the status of the booking if payment has started with this payment method but for some reason has not been finished. The default choice here is Waiting as the payment has not been confirmed. This gives you the opportunity to contact the customer and capture a payment with a different payment method.
Order Status for Successful transactions: Waiting/Accepted/Rejected/Archived - same as above but for successful payments. The default status is "Accepted".
Order Status for Failed transactions: Waiting/Accepted/Rejected/Archived - the booking status if a transaction did not go through because of lack of funds, wrong credit card number etc. The default status here is "Rejected".
Send Email for Pending Status: Yes/No - if the booking status is Waiting you may wish not to send a confirmation email to the customer, set this to "No" if this is the case.
Send Email for Approved Status: Yes/No - same as above but for Accepted bookings.
Show Billing address in form: Yes/No - require the customer's billing address in the payment form. The default selection here is "No" to facilitate quicker payment.
Show Post/Zip code in form: Yes/No - same as above but for the customer's Post/Zip code. The default selection here is "No" to facilitate quicker payment.
Debug?: Yes/No - set this to Yes if asked by one of our support staff to track problems with the payment method. This will capture and display any error messages returned by Stripe. The default selection is "No".
Use in APP?: Yes/No - this is a very important setting if you are using the PWA mobile app for your booking form. You will have to create 2 separate payment methods - one for desktop (set this to "No") and one for mobile phone payments (set this to "Yes").