Thanks to the both of you!
I think you should set it to ¥1000/mo with a ¥1,198,000 bonus.
With ¥1,198,000, the request was rejected with "年間積立可能額(120万円)を超えています。積立金額をご確認ください。" but lowering the bonus to ¥1,188,000 (¥1.2M - 12 * ¥1,000) worked. The request was accepted.
Then in November once the CC payment for Decemeber has been taken, update it to ¥100,000/mo with no bonus.
Indeed, I'll try to do it next month and post an update if that worked, in case that's useful to others.
Probably because you're using a credit card. Using Money Bridge or the securities account balance should work fine this month.
No credit card (I wish I could, to get miles!).
I had to use the "上記銀行以外をご利用の場合(ATM・銀行窓口・ネットバンキング)" section, because my main bank is SBI Shinsei and it's not supported by the easy integration options that Rakuten provides.
I could only chose the 8th and 24th of the month, for some reason.
I stopped trying to understand JP banks limitations, that's the path to madness
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