If you are creating Royal Mail Tracked, or 24 and 48 labels with Royal Mail from Bluepark, it is possible to connect the Bluepark Safe Place field to Royal Mail via the advanced settings in your Shiptheory account.
From the main menu, browse to the Bluepark settings page and click the cog in the bottom left-hand corner: 
From this section, find the "Delivery Instructions field" setting and change it to safe_place. If you do not have a safe_place field in your Bluepark frontend, please contact Bluepark to have it added. After selecting this field, save the settings. Then, when booking Royal Mail labels from Shiptheory or Bluepark, make sure to select the Safe Place enhancement. Provided the enhancement is selected, the safe place field is populated, and safe place is available on the selected Royal Mail service, the safe place text will appear on the Royal Mail label.
If you have any questions, please contact support.