1195 LINE Pay does not support your version.

Hi,

It seems to be an issue with your LINE Pay merchant account.
Apparently, you need to accept the privacy policy:

Checkout機能を利用する場合は、ユーザーにプライバシーポリシーへの承認をもらう必要があります。必ずプライバシーポリシーへのリンクをご用意してください。設定されていない場合は、returnCode:1195(LINE Pay does not support your version.)が返されます。

pay.line.me/jp/developers/apis/onlineApis?locale=ja_JP
So you'll have to check your merchant account with LINE Pay.

That's a strange way to word an error message for privacy policy. And even weirder, the english version of that same documentation doesn't mention this error message even though the rest of the text is properly translated to english: developers.line.biz/en/docs/line-pay/checkout/#checkout-flow

Hi,

I think you're misunderstanding things.
The

本APIはSandbox環境では利用できません。

message there is for the shipping inquiry API.
This API allows LINE Pay to request the shipping fee from your website once the customer enters his address on LINE Pay.
That's what the example below that text presents too.
However, the LINE Pay plugin does not use this mechanism. The LINE Pay plugin directly provides the shipping fee and address to LINE Pay.

Also, the page pay.line.me/jp/developers/apis/onlineApis?locale=ja_JP says that this specific error message will appear if the privacy policy of the account is not accepted.
It could be explained by the fact you're using a sandbox account. But I'm not sure.
We did test the plugin with a sandbox account on our end and it worked fine but it was not with the japanese LINE Pay.

What you can do is to change the line:to:in the file plugins/hikashoppayment/linepay/linepay.php
This will make it not use the Checkout API, even for Japan and you should not have the problem.